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VoIP peering – a snapshot. Henning Schulzrinne w/Charles Shen Dept. of Computer Science Columbia University http://www.cs.columbia.edu/~hgs. Overview. Review: What is VoIP peering? Why VoIP peering? Scaling peering to millions of users Challenges for VoIP peering Beyond PSTN replacement

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voip peering a snapshot

VoIP peering – a snapshot

Henning Schulzrinne

w/Charles Shen

Dept. of Computer Science

Columbia University

http://www.cs.columbia.edu/~hgs

overview
Overview
  • Review: What is VoIP peering?
  • Why VoIP peering?
  • Scaling peering to millions of users
  • Challenges for VoIP peering
  • Beyond PSTN replacement
  • Resources
what is voip peering
What is VoIP peering?
  • Definitions from IETF SPEERMINT Working Group:
    • “Peering … refers to the negotiation of reciprocal interconnection arrangements, settlement-free or otherwise, between operationally independent service providers.” (draft-ietf-speermint-res-and-terminology-01)
    • Layer 5 peering refers to interconnection of two service providers for the purposes of exchanging SIP signaling. Note that in the layer 5 peering case, there is no requirement for any intervening "Layer 5 Transit Network". Each service provider is expected to interconnect directly with other service providers, although a service provider is allowed to interconnect through another domain (ex: a federation) to act on its behalf.(SPEERMINT, IETF 65)
  • Cable Labs
    • “The notion of IP Service Peering (and VoIP Peering) … extends the relationship between network operators above the IP layer, by handling the IP-based services and applications that can be exchanged.”
why voip peering
Why VoIP peering?
  • Near-term motivations
    • avoid PSTN hops between VoIP service providers
    • codify provider trust relationships
    • bridge wait until global ENUM
  • Longer term motivations
    • no PSTN in the middle 
      • advanced signaling services
      • no transcoding  better audio quality
      • wideband audio codecs
      • video, IM, …
    • possibly increase in trust
      • smaller number of players  spam, spit 
why is voip peering needed
Why is VoIP peering needed?
  • Non-reasons
    • SIP: providers can talk directly to each other if SIP URIs are available
      • sip:alice@example.com  look up SIP server for example.com (NAPTR, SRV) and connect
      • email-like  no email peering
    • L3: probably best to avoid triangle routing
  • Reasons
    • E.164 numbering: who serves the customer with +1 212 555 1234?
      • absence of global ENUM 
    • interoperability
    • billing
session interconnect
Session interconnect

E.164

number

peer discovery

ENUM lookup of NAPTR in DNS

SIP

URI

aka call routing data (CRD)  derived from ENUM record

service location (lookup of NAPTR and SRV) in DNS

host name

addressing and session establishment

lookup of A and AAAA in DNS

IP

address

routing protocols, ARP, …

MAC

address

peering evolution
Peering evolution

VoIP Service Providers interconnect via PSTN using E.164 numbers for addressing

VSP

VSP

VSP

VSP

VSP

PSTN Plane

+4315056416

Otmar Lendl, March 2006 (SPEERMINT)

messy reality
Messy reality

Private Interconnection Network

Private Interconnection Network

sip:office@enum.at

VSP

VSP

VSP

VSP

VSP

Public Internet

Closed SIP federation

PSTN Plane

Otmar Lendl, March 2006 (SPEERMINT)

example cable operators
Example: Cable operators
  • MSOs want to avoid PSTN traversal
  • Call Management Server Signaling (CMSS) = SIP

Jean-François Mulé, IETF 63

peering decomposed model
Peering: decomposed model

domain A

domain B

draft-penno-message-flows-02

peering collapsed model
Peering: collapsed model

~~~~



~~~~

~~~~



~~~~

B2BUA

domain A

domain B

draft-penno-message-flows-02

peering authorization
Peering authorization

P1

P2

INVITE

  • On-demand
    • “email model”
    • as needed when exchanging SIP messages
    • usually, mutual TLS authentication
    • proposed SUBSCRIBE/NOTIFY key exchange
  • Static
    • established ahead of signaling
    • e.g., TLS or IPsec
    • proposed SUBSCRIBE/NOTIFY key exchange

100 Trying

SUBSCRIBE w/PeerAuth

401 Unauthorized

SUBSCRIBE w/auth

202 Accepted

NOTIFY w/P2key

INVITE

401 Unauthorized

INVITE + P2Key

INVITE

100 Trying

draft-penno-message-flows-02

role of enum in peering
Role of ENUM in peering
  • Core service: look up provider for E.164 number
  • ENUM models
    • Public ENUM: e164.arpa
    • Private ENUM: limited access to DNS records (e.g., by VPN)
    • Carrier ENUM:
  • Options:
    • resolve to subscriber SIP URI
      • +1 212 555 1234  sip:12125551234@vsp.com;user=phone
    • resolve to neutral peering provider
      • +1 212 555 1234  sip:12125551234@peering.com;user=phone
      • peering.com proxy translates to actual provider
    • resolve to carrier ENUM DNS server
      • +1 212 555 1234  enum.vsp.com  NAPTR query on enum.vsp.com
    • service provider identifier (SPID)
      • +1 212 555 1234  NXXX
enum in a nutshell

sip:bdr@internet2.edu

mailto:bdr@internet2.edu

sip:bobr_621@att.sbc.com

ENUM in a Nutshell

+1-734-913-4257

  • Take an E.164 number
  • Convert it to FQDN
  • Query DNS for NAPTRs
  • Apply resulting regexs to get list of URIs:

7.5.2.4.3.1.9.4.3.7.1.e164.arpa.

e164.arpa.

1.e164.arpa.

4.3.7.1e164.arpa.

x.x.x.1.e164.arpa.

Ben Teitelbaum, John Todd, Dennis Baron:

“ISN Numbers: Fast, Free, and Forever Yours” March 16, 2006 Spring VON, San Jose, CA

who serves an e 164 number
Who serves an E.164 number?
  • Find “point of interconnection” (PoI) for given E.164 number
  • Peering provider can answer question locally
  • Likely to have dozens of such peering exchanges and federations
    • each provider will be a member of some subset of these
  • Kludge: originating provider asks all its peering providers in parallel
    • via DNS ENUM lookup
  • Possibly federate peering providers
    • flood number information, pointing to peering ENUM
    • multiple resolutions  can’t be DNS
carrier infrastructure enum
Carrier (infrastructure) ENUM
  • User ENUM
    • “entity or person having the right-to-use of an E.164 number has the sole discretion about the content of the associated domain and thus the zone content” (draft-haberler-carrier-enum-02)
    • end user as registrant
  • Carrier (now, infrastructure) ENUM
    • "carrier of record" (COR) as registrant
  • Proposal: branch under e164.arpa:
    • 4.9.7.1.carrier.e164.arpa or
    • 4.9.7.carrier.1.e164.arpa
carrier enum
Carrier ENUM
  • COR = registrant
    • block holder allocated by National Regulatory Authority (NRA)
    • "International Networks" (+882) or "Universal Personal Telecommunications (UPT)" (+878) allocated by ITU
    • recipient of a port (service provider)
    • has been contracted by a user to route a number assigned to a user directly (without COR being in the number assignment path)
      • corporate network numbers
      • 800/900 type numbers in many countries
  • Include all E.164 numbers in block
    • avoid ability to detect listed vs. unlisted numbers
provider hiding
Provider hiding
  • Some providers worry about exposing their identity to competitors
    • competitors could target customers for marketing efforts
    • unclear if more than theoretical issue
  • Solution:
    • send calls to peering provider SIP proxy, not directly to VSP proxy
      • ENUM: 12125551234@peering.com
    • peering provider does database (or internal ENUM) lookup
challenge provisioning enum entries
Challenge: provisioning ENUM entries
  • Dynamic DNS not suitable: security, scaling
  • Options:
    • bulk upload via ftp, HTTP, …
    • EPP (Extensible Provisioning Protocol) – RFC 3730
      • XML-based protocol designed originally for domain number management
speermint discussion federations
SPEERMINT discussion: federations
  • A federation is a group of VoIP service providers / enterprises which
    • agree to receive calls from each other via SIP
    • agree on a set of administrative rules for such calls (settlement, abuse-handling, ...), and
    • agree on specific rules for the technical details of the interconnection
  • Federations have a unique identifier
  • TLS-based
    • Public Internet, SIP over TLS, federation acts as X.509 Certification Authority.
  • Private network
    • Federation builds its own network; members connect directly over this network.
  • SIP hubs / transit networks
    • Calls are routed via a central SIP proxy

Otmar Lendl, “The Domain Policy DDDS Application”, IETF 65, March 2006

domain policy ddds basics
Domain Policy DDDS basics
  • The domain is the key to the destination policy
    • Use the DNS as rule store
    • No special translation rules necessary
    • Infrastructure is in place
  • Example:

example.com. IN NAPTR 10 50 "U" "D2P+SIP:fed" "!^.*$!http://sipxconnect.example.org/!" .

“Regarding SIP, example.com is a member of the federation identified by this URI.”

  • Non-terminal NAPTR for customer domains referring to provider domains
  • Protocol agnostic
    • SIP is just a special case

Otmar Lendl, “The Domain Policy DDDS Application”, IETF 65, March 2006

longer term opportunities for peering
Longer-term opportunities for peering
  • Enterprise trunk backup management
    • PSTN as primary, VoIP as backup (or vice versa)
  • Spam/SPIT prevention
    • accountable carriers
    • trustable user identification (“caller ID”)
    • exchange of abuse information
  • Billing and settlements
    • if per-call billing
enum performance
ENUM performance
  • Busy hour traffic estimate:
    • 0.1 Erlang  2 calls/hour/user
    • 100 mio users  roughly 55,000 calls/second  lookup rate
  • Post-dial delay bounds: few seconds
    • includes signaling latency
    • DNS unlikely to be a significant contributor (except if packet loss)
  • DNS server platform:
    • OS: Linux version 2.6.11
    • 1 or 2 Intel Pentium 4 CPU 3.00GHz, 1 GB memory
  • DNS servers:
    • BIND
    • PowerDNS (PDNS)
      • Open Source Authoritative Nameserver
      • Used by 50% of .de and 20% rest of the world, including e164.org.
      • Runs on Linux, FreeBSD, NetBSD, OpenBSD, Solaris
      • Serves data from MySQL, PostgreSQL, LDAP, BIND zone files, …
    • Nominum ANS
preliminary black box test
Preliminary Black Box Test

ENUM server

Client 5

Client 1

Client 4

Client 2

Client 3

black box comparison results
Black-box Comparison Results
  • All columns denoted as Nominum are from the Nominum white paper “ENUM Scalability and Performance Testing”.
  • The last column, Nominum ANS is tested with 200M records, all the rest are tested with 10M records.
  • PDNS test uses its default settings.
itad subscriber numbers isn
ITAD Subscriber Numbers (ISN)
  • 4257*260
  • ITADs
    • Defined by Telephony Routing over IP (TRIP) [RFC3219]
    • Globally unique
    • Lots of them (256 through 232-1)
    • IANA is already set up to allocate
  • ISN resolution works just like ENUM

Internet Telephony Administrative Domain (ITAD)

locallyassigned

Ben Teitelbaum et al, March 2006

isn in a nutshell

sip:bdr@internet2.edu

mailto:bdr@internet2.edu

sip:bobr_621@att.sbc.com

ISN in a Nutshell

4257*260

  • Take an ISN
  • Convert it to FQDN
  • Query DNS for NAPTRs
  • Apply resulting regexs to get list of URIs:

7.5.2.4.260.freenum.org.

freenum.org.

260.freenum.org.

Note: We are working to ensure that the ISN root zone will be administered on behalf of the ISN user community by a neutral, non-profit organization. Following the trial, the root may or may not be “freenum.org”.

Ben Teitelbaum, John Todd, Dennis Baron:

“ISN Numbers: Fast, Free, and Forever Yours” March 16, 2006 Spring VON, San Jose, CA

isn vs enum vs sip aor
ISN vs ENUM vs SIP AOR

Ben Teitelbaum, John Todd, Dennis Baron:

“ISN Numbers: Fast, Free, and Forever Yours” March 16, 2006 Spring VON, San Jose, CA

conclusion
Conclusion
  • Peering as crucial next step for large-scale VoIP
    • weaning off the PSTN…
    • needed to get beyond black-phone service
  • ENUM as core peering service
    • needed as long as phone numbers are in use
    • slow transition from private to public ENUM
  • Peering is ENUM +
    • security associations
    • privacy protections (for carrier and users)
    • billing and settlements?
  • Peering issues
    • provisioning of E.164 records
    • which peer?
  • Need for high-performance service architecture
resources
Resources
  • ENUM: RFC 3761
    • carrier ENUM: draft-haberler-carrier-enum-02
  • tel URIs: RFC 3966
  • IETF SPEERMINT working group
    • definitions and terminology: draft-ietfs-speermint-reqs-and-terminology-01
    • message flows: draft-penno-message-flows-02
  • CableLabs VoIP Peering RFI
  • GSMA GRX/IPX Requirements
  • ECMA/TISPAN Next-Gen Corporate-Core Interconnection Requirements
  • SIP Forum IP PBX / Service Provider Interoperability
  • ISNs: http://www.internet2.edu/sip.edu/isn/