3GPP soluations comments

[Pekka Savola <pekkas@netcore.fi>]

 1.1 Scope of this Document 
     
    The scope of this informational document is to analyze and solve 
    the possible transition scenarios in the 3GPP defined GPRS network 
    where a UE connects to, or is contacted from the Internet, or 

==> s/from/from,/, s/, or/ or/

 2.2 Tunneling 
     
    Tunneling is a transition mechanism that requires dual IPv4/IPv6 
    stack functionality in the encapsulating and decapsulating nodes. 
    IPv6-in-IPv4 tunneling mechanisms are implemented by virtual 
    interfaces that are configured over one or more physical IPv4 
    interfaces. Sending nodes encapsulate IPv6 packets in IPv4 packets 
    when the IPv6 routing table determines that the next hop toward the 
    IPv6 destination address is via a tunnel interface. Receiving nodes 
    decapsulate IPv6 packets from IPv4 packets that arrive on tunnel 
    interfaces. Tunneling can be static or dynamic. 

==> implicitly this discusses only v6-in-v4 tunneling.

    This means that the IPv4 source address is taken from an IPv4 
    interface over which the automatic tunnel is configured. Examples 
    of dynamic tunneling mechanisms are "6to4" [RFC3056], ISATAP 
    [ISATAP] and DSTM [DSTM]. 

==> In the above IPv4 context, DSTM is not a dynamic tunneling 
mechanism.
     
 3.1 Dual Stack UE connecting to IPv4 and IPv6 nodes 
     
    However, if the GGSN does not support IPv6 Access Points, and an 
    application on the UE needs to communicate with an IPv6 node, the 

==> I didn't know Access Points enter to the picture; they weren't mentioned
in the architecture section in any case.

    UE may activate an IPv4 PDP context and tunnel IPv6 packets in IPv4 
    packets using a dynamic or static tunneling mechanism. Tunneling in 

==> I assume the use can connect to a different GGSN for v4 and v6.

 3.4 IPv6 UE connecting to an IPv4 node 

==> Here, it's possibly better to talk about NA(P)T-PT than plain NAPT-PT;
the latter might confuse folks.

    3GPP networks are expected to handle a very large number of 
    subscribers on a single GGSN (default router). Each GGSN is 
    expected to handle hundreds of thousands of connections. 
    Furthermore, high reliability is expected for 3GPP networks. 
    Consequently, a single point of failure on the GGSN external 
    interface, would raise concerns on the overall network reliability. 

==> Note that if NAT-PT function is implemented in the GGSN, the reliability
requirement for NAT-PT need not be higher than with GGSN: if GGSN terminates
hundreds of thousands of connections, the wording appears to hint to a
possible fact that GGSN may be single point of failure (for a more basic set
of functionlity) for them too.

 4.2 UE connecting to a node in an IPv4 network through IMS  
          
    This scenario occurs when an IMS UE (IPv6) connects to a node in 
    the IPv4 Internet through the IMS, or vice versa. This happens when 
    the other node is a part of a different system than 3GPP, e.g. a 
    fixed PC, with only IPv4 capabilities. 

    Apparently there will be a number of legacy IPv4 nodes in the 
    Internet that will communicate with the IMS UEs. As the IMS is 
    exclusively IPv6, translators have to be used in the communication 
    between the IPv6 IMS and legacy IPv4 hosts. This section aims to 
    give an overview on how that interworking can be handled. 

==> IMO, I'm not 100% sure this number of legacy IPv4 nodes *IMS*
communicates with is necessarily all that large.  If I understood correctly,
that means basically v4-only SIP phones.  Are there really all that many of
those.  SIP phones that could not be relatively easily upgraded to IPv6?  If
the number of scenarios to support were to be shortened, IMO this would be
among the first ones to go.


-- 
Pekka Savola                 "Tell me of difficulties surmounted,
Netcore Oy                   not those you stumble over and fall"
Systems. Networks. Security.  -- Robert Jordan: A Crown of Swords