The Peeredge Switch/SBC supports UDP, TCP, and TLS v1.2 as transport protocols for SIP signaling. The Peeredge Switch supports RTP and SRTP protocols for media sessions. Both Both RTP and SRTP use UDP as the transport protocol.
Transport protocols provide essential services to voice applications, including:
Multiplexing - Assigning Assign port numbers to each application, which enables the IP network to carry thousands of application messages between hosts simultaneously.
Reliable message delivery - The receiver verifies the transmission of each packet using a checksum to ensure contents are not corrupted. The receiver acknowledges the verified packet or requests retransmission of the corrupted packet. If the transmitter doesn’t receive an acknowledgementacknowledgment, it assumes the packet is lost and retransmits it. The transport layer also ensures packets arrive in sequence by inserting a sequence number.
Flow control - The receiver uses a transmission window value to provide feedback to the sender about buffer space to avoid buffer overruns and underruns.
Congestion management - When multiple losses occur, the transport layer implements a back-off algorithm that allows congestion to clear before resuming transmission.
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If any portion of the end-to-end network transport is considered not considered secure (i.e. direct Internet), then 46Labs 46 Labs recommends using TLS.
If If the end-to-end network transport is already secure (i.e. SD-WAN or MPLS), then 46Labs 46 Labs recommends either TCP or UDP. If If any customer networking devices in the SIP signaling path between the customer SBCs/PBXs and the Peeredge Switches do not properly handle UDP message fragmentation and assembly, then 46Labs 46 Labs recommends TCP.
The The Peeredge Switch supports RTP and SRTP protocols for media sessions. Both Both RTP and SRTP use UDP as the transport protocol.
Recommendations for TLS
If If the customer customer’s SBCs/PBXs support the selection of crypto cipher’s ciphers when using TLS/SRTP, then 46Labs 46 Labs recommends using the AES_CM_128_HMAC_SHA1_80 crypto cipher suite since it is considered the most secure suite supported by the Peeredge Switches.
The Peeredge Switch currently supports the following crypto cipher suites for the encryption of RTP media:
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