Voice & Video Design. Dr. Nawaporn Wisitpongphan. Traditional Voice Architecture. PBX (private branch exchange) route voice using TDM -- between company’s branches (on-net) -- between company and PSTN (off-net). **PSTN = Public Switch Telephone Network. PBX and PSTN Switches.
PBX (private branch exchange) route voice using TDM
-- between company’s branches (on-net)
-- between company and PSTN (off-net)
**PSTN = Public Switch Telephone Network
Local Loop: Pair of wires connects Central Office (CO) to office.
■ Interoffice trunk connects two CO switches. Also called a PSTN switch trunk.
■ Tandem trunk connects central offices within a geographic area.
■ Toll-connecting trunk connects the CO to the long-distance office.
■ Intertoll trunk connects two long-distance offices.
■ Tie trunk connects two PBXs. Also called a private trunk.
■ PBX-to-CO trunk or CO-to-PBX business line connects the CO switch to the enterprise PBX.
Use between the telephone set and the CO, PBX, or FXS module.
Analog signaling technique used to indicate on-hook and off-hook conditions in the network
Alternative Analog signaling technique used to indicate on-hook and off-hook conditions.
Use in switch-to-switch
Ground start requires the
closing of the loop at both
locations. It is commonly
used by PBXs.
Provide just one trunk, and let callers wait until it’s available.
Provide one trunk for every local phone line, so no call is ever blocked.
We get 3,200 calls a day (during 8-hr work time). That’s 400 calls an hour. Each call lasts three minutes, so each person can handle 20 calls an hour. So we’ll need 20 incoming lines and 20 people to answer the phones….
What’s wrong with my Logic???
Calls are not evenly distributed
Au = uHu
where Hu = Average duration of a call per user (hrs/call)
u = Average # of call requests per unit time per user
A = UAu
Traffic intensity / Channel = UAu / C
An urban area has a population of 2 million residents. Three competing trunked mobile networks (systems A, B, and C) provide cellular service in this area. System A has 394 cells with 19 channels each, system B has 98 cells with 57 channels each, and system C has 49 cells, each with 100 channels. Find the # of users that can be supported at 2% blocking if each user averages 2 calls per hour at an average duration of 3 min. Assuming that all 3 trunked systems are operated a t maximum capacity, compute the percentage market penetration of each cellular provider.
U = A/ Au = 12/0.1 = 120
U = A/ Au = 45/0.1 = 450
U = A/ Au = 88/0.1 = 880
47280/2000000 = 2.36%
44100/2000000 = 2.205%
43120/2000000 = 2.156%
134500/2000000 = 6.725%
c+1M/M/c Model (Erlang C)
With separate voice & data network
■ Data is primary traffic on many voice service provider networks.
■ Companies want to reduce WAN costs.
■ PSTN architecture is not flexible enough to accommodate data.
■ PSTN cannot integrate voice, data, and video.
■ To provide the same reliability and high availability traditionally associated with older voice technologies
■ To offer lower cost of ownership than traditional telephony
■ To offer greater flexibility than traditional telephony (remote worker, mobility)
■ To leverage integration to provide new applications (presence, IVR, contact centers)
■ To improve remote worker, agent, and work-at-home staff productivity
■ To ensure backward compatibility with traditional systems and endpoints such as PBXs, faxes, and the PSTN
Framework for multimedia protocols for use over packet switched networks
For large network: If a gatekeeper is not used, logical connections need to be configured on each gateway to connect to every single other gateway on the network.
In a gatekeeper-controlled system, each device needs to be configured with only a logical connection to the gatekeeper.
L = # of Logical Connections
N = # of Devices
Example:In a network with 7 devices, 21 logical
connections must be configured to ensure that
each device can communicate with every other device.
■ Resource Reservation Protocol (RSVP) for reserving network bandwidth and priority (low-latency) queuing
■ RTP and RTCP for transporting real-time data and providing QoS feedback
■ Real-Time Streaming Protocol (RTSP) for controlling delivery of streaming media
■ Session Announcement Protocol (SAP) for advertising multimedia sessions via multicast
■ Session Description Protocol (SDP) for describing multimedia sessions
Calculate the WAN bandwidth used at a site that will have 10 concurrent G.729 calls with cRTP and a default voice payload of 20 bytes.
G.729 codec is used: 8 kbps codec bit rate.
cRTP = 2-byte IP/UDP/RTP header.
Default voice payload= 20 bytes * (8 bits/bytes) = 160 bits.
WAN header = 6 bytes.
Voice packet size = 6 bytes + 2 bytes + 20 bytes = 28 bytes * (8 bits/byte) = 224 bits.
PPS = 8 kbps / 160 bits = 8000/160 = 50 pps.
BW per call = 224 (bits/packet) * 50 (pps) = 11200 bps = 11.2 kbps.
BW for 10 calls = 11.2kbps * 10 = 112 kbps.
= codec bit rate / voice payload size.
= (voice packet size) * (pps).
Serialization delay = frame size in bits / link bandwidth in bps
■ Network Control: For routing and network control functions
■ Operations, Administration, and Management (OAM): For network configuration and management functions
■ Telephony: Includes VoIP and circuit emulation
■ Signaling: For peer-to-peer and client/server signaling, such as SIP, MGCP, H.323, and H.248
■ Multimedia Conferencing: For applications that can change their encoding rate, such as H.323/V2
■ Real-Time Interactive: For RTP/UDP streams for video conferencing applications that cannot change the encoding rate
■ Multimedia Streaming: For variable-rate elastic streaming media applications and webcasts
■ Broadcast Video: For inelastic streaming media with low jitter and low packet loss, such as broadcast TV, video surveillance, and security
■ Low-Latency Data: For data processing applications, such as web-based ordering
■ High-Throughput Data: For store-and-forward applications, such as FTP
■ Standard: For traffic that has not been identified for any preferential treatment
■ Low-Priority Data: For traffic types that do not required any bandwidth assurance
**PHB = per-hop behavior