Cisco AS5300 SERIES UNIVERSAL GATEWAYS AS535-8E1-210-AC 数据表

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delay as voice data is received from the PSTN and transmitted to the

IP network for G.711 calls. Cisco quality-of-service (QoS) features,

including IP Precedence, Resource Reservation Protocol (RSVP),

Weighted Fair Queuing (WFQ), Weighted Random Early Detection

(WRED), and Multichassis Multilink PPP (MMP) fragmentation

and interleaving, implemented on both the universal gateway and

backbone routing infrastructure, can provide a low-latency,

high-reliability path for sensitive voice traffic through today’s

networks.

Echo control is essential for packet-switched networks to carry voice

traffic successfully. The Cisco AS5350 supports ITU-T

Recommendation G.168 for echo cancellation with a tail length up

to 128 ms. Fixed and adaptive jitter buffering and comfort-noise

generation further enhance voice quality.

The Cisco AS5350 Universal Gateway offers multiple codecs to

meet interoperability, compression, and latency requirements for a

variety of phone-to-phone and PC-to-phone applications—G.711,

G.723.1 (5.3K and 6.3K), G.726, G.729ab, G-Clear and GSM-FR.

The same number of calls is supported across all codec types to

simplify network engineering. Enabling voice activity detection

(VAD) reduces packet traffic through the network. With VAD

enabled, the Cisco AS5350 detects silence and stops transmitting

packets when callers stop speaking. Variable frame sizing provides

further control over speech packetization.

For VoIP to be a practical replacement for standard PSTN telephony

services, customers need to receive the same consistent, high quality

of voice transmission they receive with basic telephone services. For

real-time, delay-sensitive traffic such as voice, it is better to deny

network access under congestion conditions than to allow traffic

onto the network to be dropped and delayed, causing intermittent

impaired QoS and resulting in customer dissatisfaction.

Numerous QoS mechanisms exist in Cisco IOS Software to allow

service providers to design and configure packet networks that

provide the necessary low latency and guaranteed delivery

required for voice traffic. These mechanisms include tools such as

queuing, policing, traffic shaping, packet marking, and

fragmentation and interleaving.

Call admission control (CAC) extends the QoS tool suite to protect

voice traffic from being negatively affected by other voice traffic,

keeping excess voice traffic off of the network. CAC allows the

Cisco AS5350 Universal Gateway to make deterministic and

informed decisions before a voice call is established based on

whether the required network resources are available to provide

suitable QoS for the new call. CAC provides:

• Voice call admission decisions based on overall CPU utilization

and call arrival rate at the individual gateway

• Voice call admission based on the prevailing conditions in the

packet network such as end-to-end latency, jitter, or the ability

to reserve the resources required to handle the call and assure

quality

• Reporting information about only the available circuits to

H.323 gatekeepers, taking into account the circuits in use for

data, voice, or fax services to achieve higher call-success rates

Fax transmission over an IP infrastructure is an important and

growing service opportunity, especially in international markets

where fax represents a large percentage of network traffic. The

Cisco AS5350 Universal Gateway supports standards-based T.38

Real-Time Fax Relay and T.37 Fax Store-and-Forward, allowing

greater interoperability between networks. The fax detection

capabilities of the Cisco AS5350 allow service providers to offer a

single E.164 number for subscriber voice and fax services. Half as

many subscriber phone numbers are needed, resulting in significant

cost savings. The Cisco AS5350 also supports fax passthrough

upspeed for VoIP environments that cannot support T.38 Real-Time

Fax Relay end to end.

Time-division multiplexing (TDM) switching is the ability to take an

incoming call on a given DS0 and send it out on a different DS0

before the call is answered by the gateway. This feature is used in

applications such as:

• SS7 to Primary Rate Interface (PRI) grooming

• Local number portability (LNP) support in Europe

• Meeting special provisionary requirements for test calls (for

example, 911 call handling)

This feature does not require any DSP resource and hence has no

impact on the dial, voice, or fax handling capability of the platform.

TDM switching plus network-side ISDN functionality provides a

means of grooming incoming traffic and passing selected calls to

external devices, such as private branch exchanges (PBXs), test sets,

VoIP gateways, or access servers. The Cisco AS5350 is capable of

switching calls between SS7, PRI, and channel-associated signaling

(CAS) trunks.